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Yes, but they can only do that because they have special ligaments – called fetlock suspenders -, capable of fixing the leg joints, preventing them from bending while they are sleeping. “This locking system allows the animal to stand solidly on its feet, with a minimum expenditure of energy”, says veterinarian Reuel Luiz Gonçalves, from the International Equestrian Federation (FEI).
This, however, does not prevent the horse from sleeping lying down. According to experts, sleeping standing up is a form of defense for the animal, which would then be ready to escape in the face of any threat. Therefore, he only lies down to sleep when he feels he is in a safe place. The curious thing is that the horse only sleeps standing up during the first two phases of sleep, which are more superficial.
To dream, he needs to enter deep sleep, also called REM (Rapid Eye Movement, or rapid eye movement). At this stage, all muscles, including those in the legs, should be relaxed. The animal then lies down on one side of the body, with its head resting on the ground.